In vitro cytotoxicity and genotoxicity of five Ochna species (Ochnaceae) with excellent antibacterial activity

Abstract:

Extracts and fractions of some Ochna species had excellent antibacterial activity. Before considering the potential
therapeutic use of these extracts it is important to determine the safety of extracts. The cytotoxicity of Ochna
natalitia, Ochna pretoriensis, Ochna pulchra, Ochna gamostigmata, and Ochna serrulata (Ochnaceae) was
determined in monkey kidney (Vero) cells, human hepatocellular carcinoma (C3A) cells and bovine dermis
cells using the mitochondrial viability MTT assay. Their potential mutagenic effects were also determined
using the Ames testwith strains Salmonella typhimuriumTA98 and TA100 with andwithoutmetabolic activation.
The LC50 values (the lethal concentration at which 50% of the cells are killed) of the extracts on the various cell
lines ranged from 26 to 99 μg/ml. None of the plant species was mutagenic (mutagenic index values ≤ 1.59
for TA98 and ≤0.92 for TA100). In a previous study, we determined the antibacterial activity of the five extracts
against Staphylococcus aureus, Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa. From this we
calculated the selectivity index (SI) values by dividing the LC50 value by the minimum inhibitory concentration
(MIC) to obtain the ratio of toxicity to bioactivity of each extract. The plant extracts had low SI values ≤ 1.307.
This is a clear indication of non-selective toxicity, i.e. extracts are almost equally toxic to the bacteria and
mammalian cell lines used in the assays. As a result, the extracts may have limited application as ingestible or
intravenous therapeutic agents based on the in vitro findings. However, it may be necessary to also evaluate
in vivo toxicity of the extracts in animal models as in vitro toxicity does not always equate to in vivo toxicity
because of the difference in physiological microenvironment in live animals and tissue culture. Additionally, if
it is the case that the toxic compounds are not the same as the active compounds, it may be possible to potentiate
the extracts by the removal of toxic compounds and concentration of active compounds. The extracts may then
be useful for development into treatments for topical bacterial infections.